tested how baby rats responded to the pairing of an unfamiliar odor--peppermint--and a weak electric shock to their tails. The charge-laced scent attracted the youngest pups without exception while repelling their older siblings of 21 days--the age when rats become fully independent. But young rats between 12 and 15 days old either learned to love the peppermint despite the shock if their mother was present or learned to fear it if she was not. When presented with the odor later in a Y-maze, the mothered pups would invariably move toward it while their motherless counterparts would move away.The mother's presence, it appeared, reduced the level of the most common stress hormone, corticosterone, making the pups react less fearfully to the tainted scnet — or, to put it another way, her absence elevated those stress hormones, making the pups learn a more fearful lesson from the association of shock and scent. This doesn't break brand new ground. But it adds a bit of detail to the model of stress and mental health that neuroscientists and endocrinologists like Bruce McEwen have been developing. One stressor or threat magnifies the impact of the next; as you string more together (particularly in the absence of more constructive learning), you gradually tip a creature away from confidence and adventurousness and toward retreat and depression.